Such an ultrasonic motor may particularly be used as a miniature drive unit in various types of precision mechanisms in which parallel, independent forward or rotating motion of multiple movable elements is required. Such elements might be for example the collimator shield plates in x-ray machines, the closing elements of code locks, the modulators for laser or light sources, drive units for multiple lens arrays, the moving parts in chemical and biological metered dispensing apparatuses or in metering devices for spray substances.
Ultrasonic motors equipped with plate-shaped ultrasonic actuators that operate on the basis of acoustic bending and longitudinal waves are known from U.S. Pat. No. 5,714,833. In these motors, the bending wave represents a traction wave and the longitudinal wave represents a type of meshed wave. However, when a bending wave is used as the traction wave, the motor is rather inefficient and the tractive force achievable therewith for a given excitation voltage is relatively small.
In order to increase the tractive force of such motors, multiple ultrasonic actuator are combined in a pack, which is then used to drive an element to be driven. Since all of the actuators are pressed against the element to be driven in parallel, the forces generated by the individual actuators are added together. However, such a motor has correspondingly large dimensions. Furthermore, the high excitation voltage means that a corresponding excitation device is more difficult to produce and the motors are more expensive, which greatly limits their field of use.
Ultrasonic motors with a plate-shaped ultrasonic actuator, which works with two acoustic longitudinal waves are also known from U.S. Pat. No. 6,765,335. The use of a longitudinal wave as the traction wave substantially increases the tractive force of motors with an actuator. Accordingly, there is usually no need to use multiple ultrasonic actuators with such motors. Such motors also work with relatively low excitation voltages.
The disadvantage of such ultrasonic motors, in which the ultrasonic actuator is located in a separate housing, consists in that the motor housing makes it impossible to arrange multiple elements to be driven close together as they must be to function together as a compact unit. Corresponding miniaturisation is therefore only possible to a limited degree.